1. Field of the Invention
The embodiment discussed herein is related to a method of manufacturing a silicon carbide semiconductor device.
2. Description of the Related Art
Conventionally, when various types of devices are produced using a silicon carbide (SiC) substrate or a silicon carbide epitaxial substrate where an epitaxial layer is stacked on starting substrate (hereinafter, collectively, silicon carbide substrate), an ion implantation process is necessary for forming the device structures. After the ion implantation process, activation heat treatment is necessary to activate the impurity ion-implanted into the silicon carbide substrate and when silicon carbide is used as a semiconductor material, the activation heat treatment has to be performed at a high temperature of about 1600 to 1800 degrees C. Since activation heat treatment is performed at such a high temperature, when the activation heat treatment is performed without protecting the surface of the silicon carbide substrate by a protective film, the surface of the silicon carbide substrate is known to become rough.
A method of performing activation heat treatment in an argon (Ar) gas atmosphere doped with silane (SiH4) gas has been proposed as a method of reducing surface roughness of a silicon carbide substrate accompanying activation heat treatment. Further, a method of performing activation heat treatment where the surface of the silicon carbide substrate is covered by a carbon (C) film, after an impurity is ion-implanted into the silicon carbide substrate is commonly known as another method of reducing surface roughness occurring consequent to activation heat treatment (for example, refer to Japanese Patent No. 5673107). Methods such as sputtering, chemical vapor deposition (CVD), and application of carbonizing resist to the surface of a silicon carbide substrate are used as methods of depositing (forming) a carbon film.
Nonetheless, as a result of earnest research by the inventor, it is clear that in a method of performing activation heat treatment in a gas atmosphere doped with silane gas, it is difficult to suppress surface roughness of the silicon carbide substrate. Further, even in a method of performing activation heat treatment with the surface of the silicon carbide substrate covered by a carbon film, depending on the heat treatment equipment and heat treatment conditions, surface roughness of the silicon carbide substrate may occur. This is because cracks occur in the carbon film depending on the deposition method (sputtering, CVD, spin-coat method) of the carbon film and heat treatment conditions. Further, even when cracks do not occur in the carbon film, if the thickness and/or film quality of the carbon film are insufficient to function as a protective film, surface roughness of the silicon carbide substrate may occur. Therefore, to improve yield, ensure device reliability, etc., there is room for improving methods of forming a protective film that protects the surface of a silicon carbide substrate during activation heat treatment.